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    <title>Document</title>
    <script>
        var time = prompt('请问现在几点了：')
        if (6 <= time && time <= 12) {
            alert('上午好');
        } else if (12 > time && time <= 18) {
            alert('下午好');
        } else if (18 < time && time <= 23) {
            alert('晚上好');
        } else {
            alert('现在是睡觉时间');
        }
    </script>
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